The present invention relates to horizontal directional drilling. More particularly, the present invention relates to a method of installing a tracer wire segment above a pipeline segment utilizing a horizontal directional drilling process.
Utility companies commonly install non-metallic pipelines to reduce cost. A common non-metallic material of construction for a utility pipeline is polyethylene. Polyethylene pipelines are used by a variety of utilities including, but not limited to, natural gas, water and telecommunications.
Because the pipeline is non-metallic, once the pipeline is buried, it is difficult to precisely determine the pipeline's location. To aid in locating the pipeline, a tracer wire may be installed along with the pipeline such that the location of the pipeline can be detected with a metal detector or a device that detects a signal transmitted along the tracer wire. Typically the tracer wire is positioned between 6 inches and 12 inches above the pipeline to minimize the risk of lightening traveling down the tracer wire and melting or damaging the non-metallic pipeline.
In many instances, the utilities must install the pipeline under an obstacle such as a driveway, a road, a railroad track or a body of water such as a river, a lake or a swamp. Many times, the utility will employ a horizontal directional drilling process that drills a bore beneath the obstruction without causing damage to the above ground landscape where the pipeline segment is installed within the bore.
However, the cost associated with the horizontal directional drilling process are substantially higher than the cost associated with the traditional method of digging a trench and laying the pipe into the trench. While digging a trench may be less expensive than horizontal directional drilling, digging a trench harms the aesthetic appearance of the landscape. In some instances, a trench installation may not be feasible such as when a segment of the pipeline must be installed below a body of water.
The horizontal directional drilling process begins by attaching a drill bit to a length of flexible pipe. The flexible pipe is attached to a horizontal directional-drilling machine which is positioned on one side of the obstruction. The horizontal drilling machine urges the drill bit into the ground to drill a bore beneath the obstruction to another side of the obstruction. At times, the bore can be over a mile in length and having a diameter that is capable of accommodating a pipeline segment having a 12 inch diameter.
When the drill bit bores through to the other side of the obstruction, the drill bit is removed and a reamer is attached to the flexible drilling pipe. An end of a pipeline segment and an end of the tracer wire segment are attached to the reamer. The directional drilling machine pulls the pipeline segment and the tracer wire segment through the bore in the opposite direction of the drill bit. This step in the horizontal directional drilling process is referred to as the “pull back.”
As the reamer pulls the pipeline segment and the tracer wire back through the bore, the tracer wire incurs a significant amounts of stresses and strains which has a tendency of causing the tracer wire to break. When the tracer wire breaks, a new bore must be drilled beneath the obstacle and the pull back process must be repeated. Having to repeat the boring and pull back process causes an increase in the time required to complete the project which substantially increases the cost of the project.
A common tracer of wire is a solid copper wire because solid copper is easily detected with a metal detector and has a low resistance which allows a signal to be transmitted down the wire to detect a break. However, a copper wire may not have enough tensile strength to withstand the stresses and strains incurred during the pull back process resulting in the tracer wire segment breaking.
To compensate for the lack of strength of a copper wire, a solid stainless steel wire may be used as the tracer wire. The stainless steel wire has the advantage of being able to withstand a significant amount more stress and strain than a solid copper wire. However, a stainless steel wire is substantially more expensive than a copper wire and has a higher resistance which impedes the transmission of a signal as compared to a copper wire. Therefore, horizontal directional drilling companies are in need of an inexpensive but strong wire that is easily detected but able to transmit a signal along a length of the wire without much resistance.